Java 9 cleanups compatible with Java 8

See merge request !12

Added a method to remove ASM specific access flags (not defined in the JVM specification) that caused some tests to fail.

Again, this is to accomodate the "dispatchmp" test on slower
machines (it takes 14-15 seconds on a modern machine).

This may be necessary for the "dispatchmp" test to finish
on slower machines.

The race was in the code displaying the "So far received..." message.
After the check if the counter value modulo 1000000 was zero, the
value actually displayed was queried again, potentially obtaining a
different value (another thread might have incremented the counter).

To force the client to send notifications about garbage collected
objects, the client code forces the GC repeatedly and waits a bit
between the attempts.

Fix try-catch block sorter and bump ASM to 7.2

See merge request !9

This is a backport of a fix from the development branch which allows
using ASM version past 6.1, i.e., version 6.2 and later.

Minor changes to the disl.py script to use Python 3.

See merge request !7

The JVMTI documentation mentions that these references
(thread_group and context_class_loader) should be managed,
so we call JNI->DeleteLocalRef() on them.

This was a source of issues with markers which forgot to set the
delimiter prior to requesting multiple values. Instead, the
getMultipleValues() method has been modified to require the delimiter
as an argument, forcing the users of the Parameter class to supply the
delimiter on use. The BytecodeMarker, InsnNodeMarker, and the
StrictBytecodeMarker were updated to reflect the change.

Originally DiSL classes could not contain other than annotated
snippet methods. This relaxes the SnippetParser to allow other
methods to be present in DiSL class and it also only warns on
snippets with multiple annotations (instead of throwing an
exception).

This allows to combine guard classes and static methods used
from guard classes with the snippet code. This makes small-scale
instrumentation more self-contained. We should make sure that
snippet code does not try to invoke those methods though.

Split of cache lookup from finding the method via reflection
and annotations and rename the field caching the results.

Get rid of synchronization in getInstance() method and instead use
a static initializer to create the GuardResolver singleton (we should
get rid of that too, but later).

Added getOwnerName() and getOwnerSimpleName() which return the
fully qualified class name and just the class name, respectively.

Made the class final and renamed the private fields to match
the convention.

Relaxed the DiSL class parser to allow DiSL class to contain fields
without annotations. The parser previously threw exceptions, which
made it impossible to include guards in the DiSL class. The parser
should really only choke on fields without annotations that are
actually accessed from DiSL snippets.

Protobuf

See merge request !2

CI setup

See merge request !1

This fixes problem with instantiating the marker with only
a single node class.

This is to ensure that data that may still be in socket
buffers when close() is called are sent to the other side.
This mainly applies to the Shadow VM agent, because it only
sends data to the Shadow VM server and does not expect any
reply, but it is probably a good practice in general.

Simplify method that receives data from socket channel.